1. Field of the Invention
This invention relates to a receiver for a two channel television sound.
More particularly, the invention relates to a receiver being capable of receiving a stereo sound signal which comprises a first channel and a second channel, the first channel including a m(L+R)-information and the second channel including a 2mR-information, wherein R is the "right" information and L the "left" information and m any real number.
The invention also relates to a receiver being capable of receiving stereophonic as well as bilingual informations.
2. The Prior Art
Multiplexing of a second sound channel with that one usually existing in broadcasting or the multiplex transmission of TV sounds is not only useful for bilingual transmission, but also for the transmission of a stereophonic sound. Consequently, various multiplexing systems have been proposed. Some of these systems transmit a (L+R)-channel as well as a (L-R) channel, as it is common practice in audio stereophony (see: Yasutaka Numaguchi: Television Sound Multiplexing System, Journal of the asia electronics union, Vol. 3, 1970, No. 2, p. 12-21). In another stereophonic television sound transmission system different combinations of the left and right signals have been described (see: Halstead and Burden: A compatible FM Multiplex System for Stereophonic Television Service, Journal of the Audio Engineering Society, January 1962, Vol. 10, Nr. 9, p. 16-21; U.S. Pat. No. 4,048,654, col. 17, lines 5-60; U.S. Pat. No. 4,139,866, col. 17, lines 15-35). Also, in AM stereophonic broadcasting, further different combinations of the left and the right information were disclosed (see: Torick: AM stereophonic Broadcasting--An Historical Review, Journal of the Audio Engineering Society, Vol. 23, 1975, p. 803, left column).
An inherent disadvantage of all these systems lies in the fact that the correlated noise, preferably occuring with the intercarrier demodulation in a FM television signal, is distributed asymmetrically on the two channels.
To overcome this disadvantage, a method for transmitting stereophonic signals on two equivalent channels has been proposed, particularly for a two-carrier system in the television sound, whereby on the first channel a L+R-signal and on the second channel a 2R-signal is transmitted (see: Rundfunktechnische Mitteilungen, Vol. 23, No. 1, February 1979, p. 10-13; German Auslegeschrift No. 2827159). A receiver for receiving this stereophonic signal comprises a decoder having two inputs, the one of these inputs being supplied with the L+R-signal and the other being supplied with the 2R-signal. The 2R-signal is amplified by the factor 0,5 and then subtracted from L+S. Thus, the signals L and R, respectively, are obtained, each of these signals including the same amount of correlated noise.
In another device for receiving stereophonic signals on two equivalent channels, the one channel carries a 1/2 (L+R)-information, whereas the other channel carries a R-information (German Offenlegungsschrift No. 29 02 933 corresponding to European Patent Application No. 80 10 021.9). The signal 1/2 (L+R) is first amplified by the factor 2 and then supplied to a subtractor which subtracts the signal R from the signal L+R, so that the signal L results. Also, a switch is provided which either connects the R-input with the subtractor for stereophonic reproduction or the 1/2 (L+R)-input with said subtractor for reproduction of a second language in a bilingual program.
A disadvantage of these prior art decoders is the necessity of an amplification of the received signals, either by a degree of amplification of 0,5 or by a degree of amplification of 2. Still, if the amplification rate is 0,5, an amplifier must be inserted into the right channel, whereas the subtractor is interposed in the left channel. Also, the prior art decoders are not capable of distinguishing automatically between a stereo signal and a bilingual signal.